Materials contract and expand with changes in temperature. Temperature can alter not only the properties of a strain gage element, but also the properties of the base material to which strain gage is attached. Difference in expansion coefficients between the gage and the base material can induce strain between the strain gage and the sensor element Differential expansion and contraction between the strain gage element and the base element introduces errors that are difficult to correct.
The accurate measurement of both static and dynamic strain is frequently used to measure such measurands as load, pressure, torque and acceleration. Conventional strain gages are typically applied to both stationary and rotating components for this purpose but are susceptible to error induced by temperature.
Methods exists which partially correct temperature-induced errors in resistive sensors. Many approaches use a separate temperature responsive element, for example a thermocouple, thermistor or diode. These elements measure a temperature near the sensor and generate a correction signal dependent on the environmental conditions of the sensor. Other approaches involve selection of the thermal coefficients of the bridge circuit and temperature compensating elements, such as resistors to integrally balance the bridge circuit.
A problem with such prior art approaches can arise during dynamic temperature change conditions in which different areas of the sensing element experience temperature changes at different rates, such as during warmup, sudden exposure to flow fields, brief temperature excursions, or other transient temperature conditions that can often result in varying temperatures at the location of each strain gage. These variations result in errors in output due to temperature induced strain in individual gages.
Strain gage based sensors experiencing temperature gradients between strain gage locations exhibit errant output. Existing temperature compensation schemes do not remove this effect. Failure to address these effects results in measurement uncertainty.
Based on the foregoing, it is believed that a need exists for a temperature differential compensation network to measure the temperature difference between the strain gage sensor locations to dynamically correct the temperature induced error.